(1) Field of the Invention
The present invention pertains generally to the configuration of a frame or housing for an electrical device such as a motor or generator, where the frame is cast of metal and includes an integral lead channel to accommodate electrical wiring leads of the electrical device and an egress opening in the channel through which the leads pass. The lead channel configuration directs the electrical leads inserted into the channel from one of the axially opposite ends of the electrical device contained in the frame toward the egress opening at the center of the frame. A reinforcing rib extends circumferentially across the lead channel inside the egress opening and stiffens the channel while also providing a portion of a continuous circumferential surface on the interior of the frame that engages around the electrical device secured in the frame. The rib is also cast as an integral part of the frame.
(2) Description of the Related Art
The construction of conventional electrical devices such as electric motors and generators typically includes an enclosure such as a substantially cylindrical frame or housing that is cast of metal as a single tubular wall having a cylindrical interior surface and having a plurality of heat radiating ribs or fins extending longitudinally across its exterior surface. These types of enclosures, often referred to as frames, are employed with various types of machines where the radiating fins dissipate heat away from the machine contained in the frame. Where such frames are employed with electrical devices such as motors and generators, the frame is typically cast of metal such as cast iron.
The frame tubular wall has a cylindrical interior surface that is dimensioned to receive the electrical device, such as an electric motor or generator hereinafter referred to as the core device, in a tight, friction fit around the core device that securely holds the core device in the frame interior preventing any relative movement between the core device and the frame tubular wall, and maximizing heat transferred to cooling fins. In assembling the core device into the tubular wall interior, the core device can be press-fit into the tubular wall interior or the tubular wall can be heated and expanded prior to insertion of the core device therein. On cooling of the tubular wall, it contracts around the core device and thereby provides the tight friction fit that securely holds the core device in the tubular wall of the frame.
The tubular wall of the frame has axially opposite front and rear openings through one of which the core device is inserted. End caps are later secured over these openings. The end caps support bearings that in turn support the rotating shaft of the core device. Also, the end caps will also have an egress opening for the electrical leads of the core device, which are usually positioned at one of the axial ends of the core device, to pass through. An outlet box is often attached over the egress opening.
In many frame constructions, it is desirable to position the outlet box on an exterior side of the frame tubular wall intermediate the axially opposite front and rear openings. In frame constructions of this type, due to the tight circumferential fit of the frame tubular wall around the core device, provisions must be made in the frame construction to accommodate the electrical leads of the core device that extend from one or both of the opposite axial ends of the core device to the electrical lead egress opening in the frame. In the past, an elongated opening has been provided through the frame tubular wall where the elongated opening would extend axially beyond the axially opposite ends of the core device so that the electrical leads of the core device could be passed through one or both of the opposite ends of the elongated opening. A cover would be positioned over the elongated opening on the exterior of the frame tubular wall and secured to the tubular wall by separate mechanical fasteners. Alternatively, the cover would be cast integrally with the frame tubular wall. The cover would have an egress opening at its center. The electrical leads extending from one or both of the axially opposite ends of the core device would be passed through the axially opposite ends of the elongated opening in the frame tubular wall and then through the channel formed by the cover to the egress opening at the center of the cover. The electrical leads would then pass through the egress opening to an outlet box secured to the exterior of the channel cover.
A number of shortcomings have been observed in the construction of frame enclosures for core devices of the type described above. The elongated opening provided through the frame tubular wall to accommodate the electrical leads would significantly reduce the hoop stiffness or strength of the frame enclosure, thus reducing heat transferred to cooling fins. What is meant by the hoop stiffness or strength is the resistance of the frame enclosure tubular wall to circumferential or radial expansion. It can be seen that the hoop stiffness or strength is critical in the ability of the frame enclosure tubular wall to securely hold the core device in friction engagement in the interior of the tubular wall and to ensure adequate heat transfer. With an elongated opening extending axially across the tubular wall of the frame enclosure, its ability to resist radial expansion or circumferential stretching is reduced.
Also, with the elongated opening extending axially or longitudinally across the tubular wall of the frame, areas of stress concentration are created at the axially opposite ends of the opening. After repeated thermal expansion and contraction from cylic operation of the core device, cracks could form in these areas of stress concentration.
To overcome the problem of radial expansion or circumferential stretching of the frame enclosure tubular wall when the core device is inserted into the interior of the frame enclosure and when the core device is repeatedly heated-up and cooled-down, stiffeners have been added that extend circumferentially across the elongated openings in the frame tubular walls. The common thinking in the past has been that a larger stiffener extending circumferentially across the elongated opening in the frame tubular wall will provide greater hoop strength to the tubular wall of the frame enclosure and reduce the areas of stress concentration. However, because the interior of the frame tubular wall must have a smooth cylindrical surface to accommodate the core device inserted into the tubular wall, the stiffeners traversing the elongated openings in the frame tubular walls are positioned outside the frame interiors and occupy the area of the electrical lead channel leading from the axially opposite ends of the frame tubular wall to the lead egress opening at the center of the channel. The presence of the hoop strength stiffener in the channel interiors would interfere with the passing of the electrical leads from one or both of the axially opposite ends of the core device through the axially opposite ends of the elongated opening in the frame tubular wall and through the channel to the egress opening at the center of the channel. This increased the difficulty and time required to assemble core devices in frame enclosures of this type, particularly where the core devices were large and the electrical leads were stiff and difficult to manually bend and pass through the channels to the egress openings at the centers of the channels.
What would overcome these shortcomings of prior art frame enclosures would be an improved frame enclosure having a lead channel shaped to facilitate the passage of electrical leads from the axially opposite ends of the core device through the channel to an egress opening at the center of the channel, and which also provides circumferential contact around the core device and a sufficient hoop strength or stiffness of the frame enclosure to securely hold the core device therein without increasing the difficulty of manually passing the core device electrical leads through the lead channel to the egress opening at the center of the lead channel.